Non-woven and woven fabric for use as reforming catalyst

ABSTRACT

A reforming catalyst is proposed which is used when producing hydrogen as a fuel for a fuel cell from e.g. utility gas. The reforming catalyst is a non-woven or woven fabric made up of composite fibers each including an elongated carbon core, and a plurality of ribs attached to the carbon core so as to extend in a longitudinal direction of the carbon core while being circumferentially spaced apart from each other. The ribs contain a precious metal. The fabric contains less precious metal and is thus less expensive.

BACKGROUND OF THE INVENTION

This invention relates to a non-woven fabric for use as a reforming catalyst used when producing hydrogen as a fuel for a fuel cell.

Fuel cells are gathering much attention these days as next-generation energy generators. Fuel cells generate electricity by chemically reacting hydrogen as a fuel with oxygen in the atmosphere. Because of their high generating efficiency and low burden on the environment, fuel cells are considered to have limitless applications.

Hydrogen, which is scarcely present in the atmosphere, is typically produced by reacting e.g. methanol contained in utility gas with vapor in the presence of a catalyst in the form of a precious metal such as platinum.

For this purpose, JP patent publication 2002-121006A proposes a reforming catalyst containing a composite oxide of a predetermined element carrying platinum and zirconium.

But because a large amount of precious metals are used in such a catalyst, the cost for producing hydrogen as a fuel for fuel cells tends to be high.

An object of the present invention is to provide a reforming catalyst for producing hydrogen as a fuel for fuel cells from utility gas which contains small amounts of precious metals and thus can produce hydrogen at a lower cost.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a non-woven fabric for use as a reforming catalyst, the non-woven fabric comprising composite fibers each comprising an elongated carbon core, and a plurality of ribs provided on an outer periphery of the carbon core so as to extend in a longitudinal direction of the carbon core while being circumferentially spaced apart from each other, the ribs containing a precious metal. The precious metal is a precious and chemically stable metal suitable for use as a catalyst, such as platinum, palladium, rhodium, iridium or ruthenium.

From another aspect of the invention, there is provided a woven fabric for use as a reforming catalyst, the woven fabric comprising composite fibers each comprising an elongated carbon core, and a plurality of ribs provided on an outer periphery of the carbon core so as to extend in a longitudinal direction of the carbon core while being circumferentially spaced apart from each other, the ribs containing a precious metal.

With this arrangement, each composite fiber has its almost entire outer surface covered with the precious metal, so that the fabric maintains sufficient catalytic performance with a far smaller amount of precious metal used than is used in conventional reforming catalysts comprising metallic plates. Thus, using the reforming catalyst according to the present invention, it is possible to reduce the cost for producing hydrogen as a fuel for fuel cells. The fabric as the reforming catalyst according to the present invention is lightweight because it contains only a small amount of precious metal. Since the fabric as the reforming catalyst according to the invention is mainly made of carbon fibers, it is flexible and easy to work. Thus, the reforming catalyst can be used for many different applications.

The reforming catalyst in the form of a non-woven fabric according to the present invention has a much greater surface area than conventional reforming catalysts in the form of metallic plates and thus is much higher in the efficiency of catalytic reaction.

The composite fibers have preferably a diameter in the range of 5 to 100 micrometers.

By determining the diameter of the composite fibers in this range, it is possible to maximize the surface area of the fabric and thus the efficiency of catalytic reaction while maintaining sufficient strength to ensure resistance to repeated use as a final product.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which:

FIG. 1 schematically shows how the fabric according to the present invention is formed by melt blowing;

FIG. 2 is an enlarged perspective view of a composite fiber according to the present invention;

FIG. 3A is a vertical sectional view of a die for forming composite fibers according to the present invention; and

FIG. 3B is a sectional view taken along the line B-B of FIG. 3A.

Now with reference to the drawings, the embodiment of the invention is described. The embodiment is directed to a method of manufacturing a non-woven fabric 12 for use as a reforming catalyst according to the present invention by melt blowing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a polymer 10 a and a polymer 10 b containing precious metal powder are prepared. The polymer 10 a may be petroleum pitch, coal pitch, a thermosetting resin such as epoxy resin or phenolic resin, or a melt spinnable resin containing a curing agent. The precious metal forming the precious metal powder may be platinum, palladium, rhodium, iridium or ruthenium. If reduced at a later stage, the precious metal may also be a metallic salt such as platinum chloride or platinum oxide. The precious metal powder has preferably a particle diameter not exceeding 3 micrometers and its content in the polymer is preferably less than 40 percent by volume.

As shown in FIG. 1, a typical melt blow process comprises the steps of feeding the polymers 10 a and 10 b into hoppers 20 a and 20 b, respectively, heat-melting the polymers 10 a and 10 b in extruders 30 a and 30 b, respectively, feeding the polymers 10 a and 10 b into a die 40, spinning the mixture out of the die 40 in the form of fibers 11 to deposit the fibers 11 onto a collecting net of a conveyor 50 in the form of a sheet, peeling the sheet off the conveyor 50, optionally feeding the sheet through calender rolls 60, and winding the sheet onto a winder 70 as a non-woven fabric 12.

Each fiber 11 comprises an elongated core 11 a made of the polymer 10 a and formed with four longitudinal recesses having an arcuate section and circumferentially spaced apart from each other at equal intervals, and four elongated ribs 11 b made of the polymer 10 b and each filling one of the recesses so that the fiber 11 has a circular cross-section. Such fibers 11 are formed in the die 40 in the manner as shown in FIGS. 3A and 3B.

As shown in FIG. 3A, the die 40 has an axial passage 40 d having a cross-section complementary to the core 11 a of each fiber 11, and four radial passages 40 e. Each passage 40 e merges with the axial passage 40 d at a juncture 40 c. Near the juncture 40 c, each passage 40 e has a cross-section complementary to one of the elongated ribs 11 b of each fiber 11 (see FIG. 3B). The polymer 10 a is introduced into the axial passage 40 d through its inlet port 40 a in a molten state. The polymer 10 b is introduced into the radial passages 40 e through their inlet ports 40 b in a molten state. The polymers 10 a and 10 b thus merge at the juncture 40 c and are formed into fibers 11. The fibers 11 thus formed are discharged through a spinneret 40 f by hot air fed through hot air inlet ports 40 g and hot air blowing slits 40 h (FIG. 3A). As shown in FIG. 2, the fibers 11 thus formed have their axial core 11 a, which is made of the polymer 10 a, partially exposed. Thus, the fibers 11 maintain self-adhesiveness during melt blowing.

The fibers 11 are bonded together into a non-woven fabric 12, which is then calcined at a temperature in the range of 1500 to 1600 degrees C. and subjected to graphitization to allow the polymers forming the fibers 11 to turn into carbon. A non-woven fabric for use as a reforming catalyst according to the present invention is thus formed. The thus formed reforming catalyst according to the invention is, unlike conventional metallic plates, easy to work because it is a soft non-woven fabric comprising carbon fibers. Thus, it can be used for many different applications. If the polymer 10 b contains not a precious metal but a precious metal salt, it has to be reduced to a metallic element. The fabric may also be subjected to infusible treatment.

In the embodiment, the non-woven fabric 12 is formed by melt blowing. But the non-woven fabric 12 according to the present invention may be formed by any other known method such as needle punching, spunlacing or spun-bonding. Also, the catalyst according to the present invention may be a woven fabric comprising composite fibers 11. Such a woven fabric may be formed using a conventional weaving machine or by any known method.

For higher catalytic efficiency, the fibers forming such a fabric should have as small a diameter as possible. But simultaneously, the fabric has to maintain sufficient strength as an end product. Thus, the fibers forming the fabric have preferably diameters in the range of about 5 to 100 micrometers. 

1. A non-woven fabric for use as a reforming catalyst, said non-woven fabric comprising composite fibers each comprising an elongated carbon core, and a plurality of ribs provided on an outer periphery of said carbon core so as to extend in a longitudinal direction of said carbon core while being circumferentially spaced apart from each other, said ribs containing a precious metal.
 2. The non-woven fabric of claim 1 wherein said composite fibers have a diameter in the range of 5 to 100 micrometers.
 3. A woven fabric for use as a reforming catalyst, said woven fabric comprising composite fibers each comprising an elongated carbon core, and a plurality of ribs provided on an outer periphery of said carbon core so as to extend in a longitudinal direction of said carbon core while being circumferentially spaced apart from each other, said ribs containing a precious metal.
 4. The woven fabric of claim 3 wherein said composite fibers have a diameter in the range of 5 to 100 micrometers. 